Clone

Clone is exactly like it sounds. If you have an Action, you can apply it to multiple Node objects by using clone(). Why do you have to clone? Good question. Action objects have an internal state. When they run, they are actually changing the Node objects properties. Without the use of clone() you don't truly have a unique Action being applied to the Node. This will produce unexpected results, as you can't know for sure what the properties of the Action are currently set at.

Let's hash through an example, say you have a heroSprite and it has a position of (0,0). If you run an Action of:

C++
MoveBy::create(10, Vec2(400,100));

This will move heroSprite from (0,0) to (400, 100) over the course of 10 seconds. heroSprite now has a new position of (400, 100) and more importantly the Action has this position in it's internal state. Now, say you have an enemySprite with a position of (200, 200). If you were to apply this same:

C++
MoveBy::create(10, Vec2(400,100));

to your enemySprite, it would end up at a position of (800, 200) and not where you thought it would. Do you see why? It is because the Action already had an internal state to start from when performing the MoveBy. Cloning an Action prevents this. It ensures you get a unique version Action applied to your Node.

Let's also see this in code, first, incorrect.

C++
// create our Sprites
auto heroSprite = Sprite::create("herosprite.png");
auto enemySprite = Sprite::create("enemysprite.png");

// create an Action
auto moveBy = MoveBy::create(10, Vec2(400,100));

// run it on our hero
heroSprite->runAction(moveBy);

// run it on our enemy
enemySprite->runAction(moveBy); // oops, this will not be unique!
// uses the Actions current internal state as a starting point.

Correctly, using clone()!:

C++
// create our Sprites
auto heroSprite = Sprite::create("herosprite.png");
auto enemySprite = Sprite::create("enemysprite.png");

// create an Action
auto moveBy = MoveBy::create(10, Vec2(400,100));

// run it on our hero
heroSprite->runAction(moveBy);

// run it on our enemy
enemySprite->runAction(moveBy->clone()); // correct! This will be unique

Reverse

Reverse is also exactly like it sounds. If you run a series of actions, you can call reverse() to run it, in the opposite order. Otherwise known as, backwards. However, it is not just simply running the Action in reverse order. Calling reverse() is actually manipulating the properties of the original Sequence or Spawn in reverse too.

Using the Spawn example above, reversing is simple.

C++
// reverse a sequence, spawn or action
mySprite->runAction(mySpawn->reverse());

Most Action and Sequence objects are reversible!

It's easy to use, but let's make sure we see what is happening. Given:

C++
// create a Sprite
auto mySprite = Sprite::create("mysprite.png");
mySprite->setPosition(50, 56);

// create a few Actions
auto moveBy = MoveBy::create(2.0f, Vec2(500,0));
auto scaleBy = ScaleBy::create(2.0f, 2.0f);
auto delay = DelayTime::create(2.0f);

// create a sequence
auto delaySequence = Sequence::create(delay, delay->clone(), delay->clone(),
delay->clone(), nullptr);

auto sequence = Sequence::create(moveBy, delay, scaleBy, delaySequence, nullptr);

// run it
newSprite2->runAction(sequence);

// reverse it
newSprite2->runAction(sequence->reverse());

What is really happening? If we lay out the steps as a list it might be helpful:

  • mySprite is created
  • mySprite position is set to (50, 56)
  • sequence starts to run
  • sequence moves mySprite by 500, over 2 seconds, mySprite new position (550, 56)
  • sequence delays for 2 seconds
  • sequence scales mySprite by 2x over 2 seconds
  • sequence delays for 6 more seconds (notice we run another sequence to accomplish this)
  • we run a reverse() on the sequence so we re-run each action backwards
  • sequence is delayed for 6 seconds
  • sequence scales mySprite by -2x over 2 seconds
  • sequence delays for 2 seconds
  • sequence moves mySprite by -500, over 2 seconds, mySprite new position (50, 56)

You can see that a reverse() is simple for you to use, but not so simple in its internal logic. Cocos2d-x does all the heavy lifting!

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